Agreed. A founder should assume any ambiguity in a term sheet will be resolved in the investors favor (since you're very unlikely to walk away from a deal after signed). I preferred more comprehensive term sheets so that we could pin everything down while the investor was still in "courting mode".

Something we did in our later financings was to (very politely) provide an interested investor with a fairly comprehensive (~7 pages) template term sheet that had blanks for the major economic terms, but otherwise fully specified all the details of the proposed deal. This kept things from drifting off "founder friendly" after signing and had the added bonus of making offers easier to compare.