Seal Pot Connection with High-Pressure Side of Instrument

I would not connect it that way with the high side to the top

I would keep with the normal standard of the high side at the bottom

Actually zero elevation adjustment is required while calibrating the level instrument with seal pot, kindly refer to the figure below for reference,

When a wet leg installation is used, the low-pressure side of the level transmitter will always experience a higher pressure than the high-pressure side. This is due to the fact that the height of the wet leg (X) is always equal to or greater than the maximum height of the liquid column (H) inside the tank.
When the liquid level is at H meters, we have:
Phigh = Pgas + S H ⋅
Plow = Pgas + S X ⋅
∆P = Phigh - Plow = S H ⋅ - S X ⋅
= - S (X - H)
The differential pressure ∆P sensed by the transmitter is always a negative
number (i.e., low pressure side is at a higher pressure than high pressure
side). ∆P increases from P = -S X ⋅ to P = -S (X-H) as the tank level rises

from 0% to 100%.

If the transmitter were not calibrated for this constant negative error (-S.X), the transmitter output would read low at all times. To properly calibrate the transmitter, a positive bias (+S X ⋅ ) is needed to elevate the transmitter output.

BUT IN CASE IF WE DO NOT CALIBRATE THE LEVEL TRANSMITTER, THEN I THINK WE CAN SWAP THE LP & HP. But i don't know it is a correct assumption.

want I do when calibrating a drum level tranmitter

is frist apply to the lowside the pressure of the wetleg which is constant eg the elevation pressure and calibrate the tx to 4mA for 0% level

I then minus the elevation pressure from the pressure range of the tx this is all done on the low side of tx and highside open to atomasphere with this pressure I calibrate the tx to 20mA for 100% level

but when installing the highside is still at the bottom of tank as this is the best Standard that should be keep to in the Instrumentation trade

I hope this helps as you can tell as a Instrument tech I dont like transmitter being set up with the high side to the top even though it can be with transmitters where the output can be reversed

If you swap leads the level would read 100% when the steam drum is empty and 0% when full.

We use the same set-up in your picture and just calibrate so that the pressure of the low side being full of liquid will make the instrument read 0 when the drum is empty.