No, there's a flag like filter_maxrels that lets you control the number of relations msieve uses.
TD 100 vs TD 110 shows you the effect of using higher target densities for a given set of relations the difference is not very big. A higher density matrix is slightly tougher to solve than a lowerdensity matrix of the same size, but matrix size affects timetosolve much more.
More relations > smaller matrix.> shorter LA time.
Higher TD > makes sure you have enough relations for a reasonably small matrix.
When filtering with msieve, let's say you have 190M relations. TD = 90 might build a matrix 11M in size, while TD 110 fails and asks for more relations. If you use the full 220M relations, TD 90 might build a 7M matrix, while TD 110 builds a 6.5M matrix. The idea is that choosing TD = 110 makes sure you avoid the situation where a matrix barely builds and is quite large (e.g. 11M for this current factorization).
If you actually try these tests, let the matrixsolving step run for 1% completion, and note the ETA (ETA is pretty stable by the time 1% is done). The TD100 and TD110 ETAs won't be very different, I expect.
