XPS insulation behind walls - small gap OK?

OK guys here's a question for ya'.

I'm about to start gluing 2" XPS against cinderblock walls before framing in front of them.
Most types come in 8'x2' strips. Turns out my joists are about 7'4.5" from the slab.
So I'll have to trim them down, no big deal, that leaves ~7.5"x24" scraps.

Now, it turns out that the rest of the basement could also use having the rim joist spaces insulated - did that on the to-be-finished portion with 14"x9" XPS blocks.

Sooo.... as expensive as 2" XPS is, I'd like to make use of all this scrap.
Now, I could use that scrap from the trimmed walls if I adjust both a little, maybe to 7'3" and 8.75" or so.

The question is - that leaves my wall insulation just a little short.
Where would be best to put the gap - up top, just below the joists, so the XPS sits on the slab, or on bottom, so the joist "corner" area is better sealed?
Keep in mind there will be a top and bottom wood beam covering it with the framing anyway.

 

The foam board is to cover the block wall against the inside air getting to it---- air tight- which is why you sealed the seams........ No gaps, not even behind the wood plates. You used p.t. wood on a poly sill sealer for a thermal and capillary break, right? Use them on top of the short wall p.t. plate for that purpose: Pressure-Treated Sill Plates and the Building Code | GreenBuildingAdvisor.com

Gary

 

Isn't it recommended that you only insulate the wall 12" below the soil line?

 

I've never heard that... ? In this part of the basement, it's all below grade.
The cinderblock wall goes "all the way up", 7'3". Then a 1.5" board on top of it (unfortunately in the 60s they didn't use PT), the joists and rim joist sit on top of this plate.

I haven't done nay framing yet or put down a bottom plate, that would come after I glue the insulation up (right?), but yes I plan to put a capillary break beneath the PT bottom.
If I cut the XPS to 7'3.5" and put flush on the ground it would cover all the cinder and the cinder/plate junction at the top of the existing wall...

 

Not my area of expertise but I have insulation on below ground walls put there by the builder - he doesn't seem like the kind of guy to spend money on something which isn't recommended

 

http://www.quadlock.com/technical_li...Insulation.pdf

Note the foam board is R-10 for EXP and the f.g.batt, R-11, or R-13 will get convective loops to degrade the insulation, pp. 45-48: http://www.buildingscienceconsulting...Measure_Up.pdf

And some still leave a gap at f.b./f.g., lol.

Gary