I have a set of primers designed by somebody else on the basis of Arb Silva SSU database (specifically, all are matching different fragments of 16S rRNA). The issue I have is that I cannot reproduce the depth of the coverage these primers should have according to the papers describing them with anything else than TestPrime server, Arb Silva's own software. I've tried e-PCR and MFEPrimer2.0, both with quite liberal conditions. I attempted to catch the sequences these primers _have_ matched in the real world PCR (I have amplicons already sequenced) and still I don't get enough coverage (like 5-10% of the things that are there). Is there anything I'm missing here?