You HAVE to disable turbo if you want to respect the TDP value. The TDP value is always given for base clock.
I have a similar configuration, 2400G + asrock b450 itx, and the following occurs (with no clock change) under a Prime95 (blend) run :
- stock voltages / turbo ON : cpu 1.34v, soc 1.09v, 3.7Ghz, 109W
- cpu -0.1v / soc -0.035v / turbo ON : cpu 1.33v, soc 1.09v, 3.9Ghz, 108W
- cpu -0.1v / soc -0.035v / turbo OFF : cpu 1.18v, soc 1.05v, 3.6Ghz, 88W
(The wattages above are given for the whole configuration of course)
So, if the turbo stays ON, the cpu/soc clearly use the voltage/wattage margin you give them (by reducing the voltage) to boost even higher, thus cancelling any benefit you could get on consumption/temp.