Is it not reasonable to ask for a seat in every investment?
A board seat? Absolutely not, you’re a minor investor.
A pro rata opportunity? Maybe but why wrangle 50 angels when you can have 2 firms cover it?
Too many investors, too few seats
Very few of the startups I’ve worked for have given board seats before Series B.
A general rule of thumb is that you have 3 board members at the seed (1 non-CEO founder, the CEO which is typically another founder, and the lead investor). So you have 1 seat available for investors, whereas you may take 5-20 checks. Not everyone is getting a seat.
At the A you usually expand to 5, adding the lead of the A round and an independent board member. Beyond that, it’s common for the earlier investors to get replaced on the board in future rounds and maintain observer rights.