NPT thread cutoff question

I installed a new radiator, and now the temp sensor doesn't reach the water. The bung in the radiator is 1/2 NPT, and the adapter is 5/8-18 [or 3/8 NPT] i thought about just cutting off some threads from the 1/2 inch male brass adapter that goes into the header tank, but as the NPT threads are tapered, I'm not sure that would get it any further into the tank [As tight as i feel comfortable twisting it in, almost half the adapter is still above the bung] Does anyone know if cutting down the threads will work? I am running out of time, and don't have a spare, so I need to get it right, or leave it alone [I have a backup sennsor on the CDS, but it is difficult to read]

Thanks

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