Strange things

I have 2 diesel heaters. One is a 8kw one from vevor and one is a 5 KW from AliExpress. The 8kw i bought this unknowing that 8kw didnt exsisted. The other one i bought after a few months and was planning to upgrade it. So i did. Bought a controller that you can tune among other things. Well the first heater had bluetooth and was getting like 215 c on the burner. When i tested the 5kw with the original controller i got 230 c on the burner.... Nice. I then installed the tunable controller and it is not this hot. I tuned it like you supposed to, turned fan speed down because 5000rpm is wat to high. I am now at 3.2 hz on 3500 rpm and i Cant get anything lower. Even the lowest setting is 2.3hz on 1500 rpm ... But the real heat ... Is gone ... Is theres something i am missing?