I don't increase the block size, I increase the number of blocks. If a double asks for 30 blocks (5x6) and I want it larger, I go 8x9 making 72 blocks for the kingsize. I realize it sounds like alot more work, and it is. The other option is adding sashing between all your blocks,but, that tends to loose the effect of the pattern at times. This is just my method. Probably someone on here has an easier solution, so I'll be watching also.