Not really. Well. ...... OK, it's not that simple.
"Large" meaning a fairly full 1.060 beer, with about 14 lbs total grain weight, no problem at all. Easy.
"LARGE" meaning the 08-08-08 RIS I brewed yesterday, 1.088 with 17.7 lbs grain weight ... it was still decidedly under the max volume of my mash tun, but it was on the full side. I couldn't go higher than probably 19, maybe 20 total lbs grain weight.
For the RIS, my dough-in was 5.5 gal, and my sparge was 3.75 gal. The sparge was definitely close to overflowing. Two 2-gal batch sparges could have been helpful.