@muttonup, to specifically answer your question: Yes; where both edges need support, it is best practice to provide blocking in plane with both upper and lower surfaces.
The rest is to expand a little bit:
Yes, that works to provide backing for the two planes. Although, doing the same thing in a different way is better for preventing differential movement between planes as well as being typical in the trades; you're going to get more stiffening out of an oversized piece of lumber beveled at the correct angle on the top edge so you have full height blocking for both planes.
Keep in mind that blocking, in the context of load bearing, is typically not necessary when the span between joists does not exceed that required for meeting the needed load rating for the sheet good.
Can I ask what drove you to decide to add blocking? Are you working off plans? Generally for new work rather than renovations, blocking for stiffening would be an unnecessary expense unless you're over-spanning your materials, and one would hope not to mess around with that unless you're working off engineered plans...?
Some notes to chew on:
- You wouldn't use H-Clips for a flat or low slope roof that has engineered plans calling for solid blocking. H-clips will transfer some of the deflection from one sheet to another, but it will still allow for cavities to form with a great enough load difference between sheets.
- If you would still need to block a tongue and groove sheet to meet the right load rating, you should just by conventional plywood and save the money. If T&G does meet the load requirement without blocking, you should save yourself time and skip the blocking, going with the T&G subfloor (after all a low slope roof is a deck, just one for the birds) to save the money on the blocking and skip a step. There is a learning curve to installing T&G.
- whatever route you take, make sure your fasteners are long enough to penetrate through the sheet good, through the sleepers, and bite the required depth into the joist itself.
- In the event that you are working off plans, a common issue for laypeople is to find that you are misinterpreting those plans. Where it calls for blocking, or noggins if that's what you are hard on calling them, the blocking may just be for stiffing the joists, and not extend up to the plane of the top of the sleepers. Take a look at the picture under the header "Step 3" in this article.