Heat issues in BP terrarium

Hej,
i have some heat regulation issues in my ballpython terrarium. I proof-ran the terrarium for over a month before i got the snake, but sadly some issues still came up when i actually got it. I switched out my old heating lamp setup (Arcadia Clamp Lamp + Arcadia DHP 80W) for a top-mounted system (Arcadia Lamp Holder + Heat Guard + Arcadia DHP 80W) because my snake kept trying to climp onto the old heat lamp guard and it seemed too risky for me.

However, now it suddenly has become very hard for my DHP to heat up the basking spot like before. I have a wooden terrarium (120x60x60). The DHP is connected to an on/off thermostat, the temperature probe is within a wooden log. With my old heating lamp setup, it would easily reach over 35 degrees, and i toggled it down to shut off when reaching 32.8 degrees & to turn back on when it was around 32 degrees. Now - it barely reaches 32 degrees anymore. My current settings are: turn off when reaching 32 degrees, turn back on when reaching 31.5 degrees. However, it will keep sinking to sometimes under 31 degrees, then get stuck at 31.2 degrees for over an hour until it will properly rise up to 32 degrees again. This whole cycle repeats itself over and over - due to the long "on" periods all the humidity keeps being sucked out of the terrarium. It is very frustrating. Do any of you know what could be the possible cause for this problem?

I checked the thermostat probe multiple times, but it seems to work fine. The DHP is very hot and seems to be working like before, but without the reflector dome it seems to not heat up enough. The cool side on my terrarium is still around 22-24 degrees, so it is not too hot or cold. The basking spot temperature is around 35-40 degrees (wood!), but the inside of the log just does not get to 32.8 degrees anymore.. Is there anything i should improve in the basking spot setup? Or any ideas on why the DHP doesnt get hot quickly enough?

I hope that was not too confusing, here are both of the setups:
OLD SETUP (reached heat easily)

NEW SETUP (struggles to reach 32 degrees, gets stuck on 31.2)

Edit: On both pictures, the distance between DHP and the temperature probe inside of the log is around 25-28 cm

Hi!

My initial thought is that the metal dome helps to reflect excess heat from the DHP downward. If that is the main difference between the two setups the argument is sound.

If the dome can't be used in the newer fixture, you can either raise the log slightly or lower the DHP a few cm and reach the previous temperatures again. 

Question: What is your BP's behavior like? How much time does it spend in the log during the day and night?

The DHP has its strengths as a complementary heat source at night (due to not giving of any significant levels of visible light), however during daylight there are better solutions for heating like halogen. They produce more IRA and IRB than the DHP.

BR
Niklas