HTP/PLA Hybrid - HTP Washes Out Ignition

This month, in an effort to get maximum thrust with minimum hardware, I ran two tests without the check valve and with a 7.5 mm nozzle throat diameter. The HTPE tank pressure was 140 psig. The first test streamed PLA out the nozzle and the second test blew up. Calculations show that the ignition surface flux (ISF) was ~ 0.3 gm/cm2/sec as compared to ~ 0.2 gm/cm2/sec on previous test using the check valve. Last month, the two successful test without the check valve was with the same ISF of ~ 0.3 gm/cm2/sec but with a nozzle throat diameter of 6.0 mm. I surmise that the smaller throat diameter slowed the flow rate enough for ignition to occur while the larger throat diameter did not. After careful consideration, I have decided to add the check valve back into the plumbing.