performance - Web Api Owin Hosted - Throughput dropping -

we've copied api have being iis hosted console app (to hosted owin + topshelf service) , have been performance profiling 2 hosting options using jmeter.

we throw 18 threads @ apis , differing results iis hosted vs console hosted, follows :

response times through iis slower. isn't surprising pipeline in iis more involved.

throughput through iis consistent, i.e. don't see significant increases/decreases in throughput (we achieve 5500 requests/responses per min)

throughput when hosted in console app starts off high (20,000 per min) degrades approximately 4,500 per min on 10 minute period.

we're trying determine cause of throughput drop when hosting console. why start 20,000 requests per min (presumably calculated on initial response times when hasn't run minute) degrade 4,500?

other things of note, cpu isn't concern. it's fluctuates start settles below 30% available, , memory average 1.34gb on 4gb ram machine.

why might throughput in iis stable , why degrade when hosted in using ms owin hosting through console app (given stable cpu , memory)?

incidentally we're trying isolate pieces of code cause degradation.

any thoughts on appreciated.