The X-15 famously used a pair of steel skids as the main landing gear rather than conventional wheels, which saved weight, allowed the skids to be mounted externally (where wheels and tires would have been destroyed) so they didn't take up internal space, simplified the extension mechanism, etc. However, they were also mounted very far back compared to most conventional tricycle-gear airplanes. Rather than being just a little ways aft of the CG as usual, they were way back under the tail. This caused some unusual behavior on landing - in addition to giving the pilot almost zero pitch control as soon as the skids touched (since they were directly under the tail, the stabilizer had no lever arm to pivot around them), it did weird things to the landing loads. From NASA book SP-60, "X-15 Research Results":
[T]he extreme-aft location of the main landing skids on the X-15 produces dynamic-response characteristics during landing that are as unusual as the gear itself.
The primary cause of the unconventional response is the craft's downward rotation onto the nose gear immediately following the main gear's touchdown. Significantly, this movement onto the nose gear causes a subsequent rebound onto the main gear, providing a much higher load there than that at initial touchdown. In addition, the nose gear encounters loads that are two to three times greater than at either of the main-gear skids. Another unique feature is that the gear loads achieve about the same maximum level whether the pilot "greases-it-on" or lands with a high rate of descent. These new gear characteristics have not been without problems. Much study and analysis of the dynamic response of the airplane during landing has led to strengthening the gear and back-up structure and modifying the nose gear so as to provide greater energy absorption.
In other words, there was actually a much higher load through the struts after the nose gear touched down when it settled back than the load from initial skid contact. NASA tech memo X-639 (19630002688 in the NTRS) even comments that if the skids were moved forward it would behave more like a regular fighter jet, but doesn't take that thought any further.
So... why did they choose to put the skids way back there rather than close behind the CG? Was it for better directional stability at touchdown with a sucks-at-low-speeds vertical stabilizer and rudder? Or was it just to provide clearance for the ventral fin stub at high landing AoA while keeping the gear short? Or, was it simply that there wasn't room left for landing gear and the required internal structure at a more conventional location? (Or as it often is, a combination of these or other factors?)