Seeing as the Paroches required only four pillars, why did the entrance to the Ohel Mo'ed require five?
Oznayim la'Torah (in Pasuk 32): Because, whereas the former where located inside the space of the Mishkan, the latter were located on the outside, in line with the boards of the north and south walls 1 - so that the three spaces between the four pillars of the Paroches were equal to the four spaces between the pillars of the screen at the entrance.
Oznayim la'Torah #2 (in Pikudei, 38:27): The Paroches ought to have had five pillars, and the reason it had only four is because the sockets of the Paroches were made of silver, 2 and, bearing in mind that there was exactly one hundred Kikar of silver - based on the six hundred thousand who were counted - there was not enough silver to make the extra socket.
