When they arrived and told us their plan, NWS (then RWM) told us "We think we can fit it into 1 square kilometre." That was conditional on locating the admin offices in Mablethorpe.
However, two other organisations have staked claims on part of the land since then.
Viking CCS wants to connect a CO2 pipeline from Immingham to the LOGGS pipeline. Their plans include a control room and a vent stack. This will occupy at least 200 square metres, not to mention the pipe, which can't be built on top of.
Mablethorpe Flexible Generation plan to build a Gas fired power station on what was the Visitor Centre and National Grid Offices. This will require laying pipelines to the National Grid connection.
As you can see this will take a quarter of the proposed site out of the equation. Whether more facilities are moved off-site or not it still means that they will need more land for their dump.
I don't want to see a nuclear waste storage facility there either, but I don't think you're going to win any arguments by misrepresenting the facts - I've just quickly copied your sketch into Google maps and the outlined area is 1.2km square, so I think that they can shoot down your argument by showing that they can lose the 200m square and still fit it in there. My experience with planning objections is that the more spurious arguments that people make, the less likely they are to be taken seriously. You need to make two or three strong points, backed up by evidence, or you just end up in the "loony NIMBYs" pile and they judge your objections …