The range hood should cover most of the range surface; many designers specify an overhang of up to three inches on both sides. By those measures, you're six-nine inches short on both sides.

The usual height from top of the range to the bottom of the hood is 30", but up to 33". To calculate whether you can go up to 36" and still have sufficient suction (which also depends on how many turns you have to the exterior) you should consult the range and/or hood manufacturer.

Different hoods specify different clearences. My Independent is a massive 1400cfm [enough to hold a cloth dish towel up, if you place about half of it against the baffles], and specifies a clearance above the range of 30 to 36 inches. My builder hung it a little high-- 37 inches-- but it works just fine.

This is against the wall, though: an island hood is different because the air can enter from either side of the hood enclosure, and are a little less efficient for that reason.

I do agree that a somewhat larger enclosure is more effective than a smaller one: I have a 56 inch over a 48 bluestar, and wouldn't have minded if it were a little larger yet. With the van on high, I can grill a steak on the built in and barely smell it from 5 feet away.

barely smell it from 5 feet away

But can you HEAR anything?

We rarely use our 600 cfm Best at anything other than low speed. At full blast, it's 12 SONEs. Even Best's maximum power unit is "only" 1,200 cfm.

I have a remote, roof mounted blower that's loud but not awful. You only need high speed if you are grilling, and that's a fast enough process that conversation isn't difficult. At low speed [Independents are 3 speeds, not variables] you know it's there, but it doesn't make you raise your voice.

A 150 cfm fan 'standard'? Even those horrible little OTR micros blow more than that, and they are completely ineffective. There's formulas for figureing how many CFM you need over on the Appliance and Kitchen forums based on the BTUs your range can throw. Since such formulas assume you are going to be using every burner on full at the same time, they are pretty much overkill, but since I have [and use] the built in grill which flames up from time to time and have a hard to clean beadboard and beam ceiling, I chose to go with the biggest residential hood I could find.

At less than maximum speed with 4 steaks on the grill, you can see the smoke swirling inside the hood enclosure, which to my mind means some of it is escaping. At high speed, it's instantly gone.

A vent for makeup air directly under the stove creates a column of moving air that also helps contain the smoke.

For a 48" range, (especially considering a 36 height above burners) a 54" wide hood is called for. You will need at least 1400 CFM fan. A hood narrower than the range is absolute nuts.
Casey

If you want to be able to see across the island you should use a downdraft exhaust or raise a standard overhead hood and live with the results or add a larger fan to a standard hood and wear earplugs. It's a matter of preference. If you really want to capture as much of the cooking odors, smoke, etc. as required a commercial kitchen, the hood would have to extend 18" beyond the range so you would essentially be standing under it and the fan would be located outside probably on the roof.

There is a price to be paid for putting cooking equipment in a home that emulates professional cooking equipment. Of course, a real hotel/restaurant range would quickly drive you out of the kitchen; I know, I owned one once.

A 36" wide hood is totally inadequate over a 48" range, especially on an island. In terms of height off the range, you need to check the hood manufacturer's specs. My hood is only 2" higher than the specs (2" higher than the highest recommended, but 4" wider than the range) and I believe it affects performance. I set it that high because DH is tall. Dumb on my part.

Don't forget to plan how it will vent out.

"I can't imagine why anyone would really want such a big vent fan. Isn't 150 cfm the average stove vent fan?"

A 'commercial style' gas stove will often have burners rated at a minimum of 15,000 BTU/hr each.
A 30 inch stove has four, a 36 inch can have 6.
If you do any pan searing or other high smoke cooking a decent size hood is required unless you want a house full of smoke and grease.

Only the newest houses are sealed well enough to matter.

A rule of thumb for sizing exhaust fans for gas ranges is 1 CFM for every 100 BTU's of output.