Your point is that when a company has a huge outstanding share position, it may be harder to obtain a higher premium, because the increase in market cap associated with said premium may not be justifiable from a valuable position.
The premium % is the same a given % (let's say 100%) is justifiable at 400MO/S as at 40m O/S ... since the total payment is the same (let's say: 600M), the buyer will not be influenced by the share count it does not care of it.