I can really see that what you are describing and illustrating, on the surface, appears to be even less than an entire topper and therefore would justify it being the same price.
But you should also consider that the majority of skill & expertise goes in to the contouring & ventilation of the front section of a hair piece.
What you are asking for, is for that to be duplicated twice and then joined together.
I'm no expert, but I imagine that there would be more work involved in doing that, than just the standard creation of a single hair piece.
There may be other companies that might be willing to take on such a complicated specialist request, but not at the lower price you would be paying through Toplace and therefore you would probably wind up paying more per section.

Please try and remember that even though your piece is very small, when it comes to it needing a replacement, we're all in exactly the same position.
But its the price we all pay to get what we want, no matter what size piece we need.
My custom size is probably 2/3 of a standard topper, but I don't to pay 2/3 of the standard price.
I pay what I'm happy to pay, to get what I need & want.

Unfortunately, your request is a niche one and therefore you are unlikely to be able to benefit from the sort of discounted prices that can be applied to larger volume, more mainstream demand.
My suggestion is that you get your initial piece made, try it, consider (if necessary) future alterations and then possibly negotiate a discount for a multiple order, further down the line.