likely, the 1/4" rod is incapable of making the bend into the tank, the dipstick blade is over 1/4" likely around 10 or 12mm wide, so 1/4" (6ish mm) should fit easily, but it would have to make the bend to do so.
you do NOT have 1/2" (just under 13mm) into the pan though.
instead of the tube heaters, try a magnetic pan heater.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!