Not necessarily, in the UK lighting enthusiasts are quite familiar with the SOX lamp, but for the new comers to SOX, I’ll explain the best I can!
Nearly all of the low pressure sodium lamps you see today are of Philips’s Hamilton construction, where as the dimples along the tube are filled with metallic sodium and as Rich says, running a 90/135 cap up would pool all the sodium to the u-bend.
However, Thorn’s SOX lamp from the Melton Road plant didn’t have these dimples and all of the sodium filling was exactly in this area of the u-bend!
And as far as I can remember growing up with SOX, very few of Thorn’s SOX ‘red burned’, even if you ran a Thorn 135 watt SOX cap up the sodium would be at the u-bend anyway!, it was there from the factory!
Saying this though, Philips lamps have rather higher doses of sodium in so I don’t know how this would affect a Philips lamp?, I have plenty of Philips 90 watts, but have never tried one cap up?
If you wish to try this in the future, I’d try it with an old lamp, (depending on how many you may come across as your collecting), but not with a new one.