the most MDMA (usually) you will EVER find in one pill, is around 150mg, at least in the US. Or even if it were 200, or even 300 (which is not the case), that by itself would be a tiny, tiny pill. So, its not like a bigger pill contains more mdma. in fact, most small pills IME are usually stronger, however this is not always true, obviously. But the point is, the size of the pill means nothing at all. They can fit a shitload of MDMA in what is prolly the size of like, a few microdots if there was no filler.
So, its just a way of your dealer getting you more hyped to buy the pill, or pay more for it. Do not fall for that shit.
Oh, and I noticed that many pills that were offered to ME and were marketed as "double/triple stacked" were methed the fuck out.
I think ill start telling people I got quadruple stacked pills. 40 a pop =P
EDIT: DAMMIT SOMEONE ELSE ALREADY USED "QUADRUPLE STACK" BUT I SWEAR I WROTE THIS BEFORE I READ THAT POST. LOL