I agree with the OP, especially if there's a colon tube to be inserted. About a week after my last enema, my colon's pretty full, but not impacted, since I have to take psyllium husk every day. I have a 1,2 m (48") Fr 42 OHP silicone colon tube. This is long enough to reach my caecum if I can get it around the splenic flexure. But that's a big IF! A full colon (I have a measure of megacolon) means it is nowhere narrowed, being full of faeces. I also note that the transverse colon sags downward from both the splenic and hepatic flexures. This sharpens each bend, making it harder to get the tube in.
So having lubricated both my bum, inside my rectum and the tube itself, I first slide the tube, admitting small amounts of soapy water (the lubricating soap is important, too) up as far as it will easily go towards the splenic flexure. There I let a bit more water in. I don't have much of a sIgmoid one left (I think I wore it out) and the tube goes past it without difficulty. Then I hold it in position and hyperventilate until I almost feel dizzy, and standing with feet apart, I bend as far forward as I can and simultaneously empty my lungs, hold my breath and suck my diaphragm in as hard as I can, before thrusting the tube smoothly into me. Because the bending forward plus the sucking in of the diaphragm, straightens out the sag of the transverse colon, the tube, which is quite flexible, goes easily round the less acute splenic flexure and into the transverse colon. Breathing again, I admit more water as I push the tube toward the hepatic flexure. There I repeat the process until the tube is fully into the caecum.
After I'm sure it's fully in, I adjust the solution flow so that five litres takes about ten minutes to flow in. There's never a cramp; in fact I can and do read a book while filling. At the end, of course, I'm as tight as a drumhead and uncomfortable because of it. When the siphon bucket gurgles, I shut off the delivery tube and detach it, leaving the colon tube inside me while I hold (for ten minutes if possible. When the holding is over, I pull the colon tube out. I can tell if it kinked (and I failed!) at this point, because there will be a hesitation (a slight jerk) if it did. But it usually comes out perfectly smoothly and the expulsion is pure delight!
On the subsequent rinse enema of plain water it is harder to get the tube in, but even more important for a proper clean out. But I do sometimes manage it!
Johnny