UK First house purchase - Amount solicitor has requested is greater than the amount I am expecting

I am currently in the process of buying my first house (UK), and am nearing the point of exchange of contracts. I have started transferring funds to my solicitor ahead of the exchange, but have noticed something that’s raised a bit of a ‘red flag’:

I obviously have my mortgage in place, and that will be covering the larger portion of the cost of buying the house- the rest is what I have saved over the years. Let’s say, for arguments sake that I’ve gone with 20% deposit, 80% mortgage.

My solicitor recently sent me ‘Request for funds’ in order to exchange the contracts, and I have started transferring money over to them.

However, I noticed that the amount that they have requested is slightly more than I was expecting- they’ve requested roughly £2,000 more than what the value of the percentage I am using my savings for works out to (with the rest obviously coming from the mortgage).

I have emailed them to clarify this, but I was surprised that a solicitor would get this basic bit of maths wrong…

I asked this question about my solicitor implying that they would make changes to a document I had signed after signing it on the Law StackExchange site, and the person who answered it mentioned that "there is so much incompetence in the legal ‘profession’" in reply to one of my follow up questions in a comment… which I was really surprised at.

The difference between 20% of the property value, and the amount they’ve asked for does not equate to the amount that their legal fees comes to… Have they just made a basic error here in the amount that they’re asking me to transfer, or is it likely that there’s something more sinister going on?