To your point, a search through the CSRs for the unit netted a total of 17 men reportedly Killed in Action (KIA) at Iuka, plus four more who reportedly Died of Wounds (DOW) on the date of battle: 19 Sept 1862, as well as one more DOW by 25 Sept 1862 (Lt. W.F.F. Wynn, who was "mortally wounded" during the fight). Those men comprise a total of 22.
But, there's is one other man (Pvt Wilson Hill) whose records state that he was "supposed dead" at Iuka, and he has no other records beyond that date to contradict that report. That makes a revised total of 23 men from this unit who'd be among those most likely to be buried in the mass grave in the Shady Grove Cemetery at Iuka. That one-time "ditch" appears to have been an active burial site for about a week following the close of battle, and holds the remains of 263-265 otherwise unidentified Confederate soldiers.
In addition to the list posted previously, the following seven men of the 27th TX Cav/1st TX Legion also died at Iuka, but their records don't necessarily support them being included in the mass interment due to the later dates of death (more than 10 days after the battle), or they lack a firm date of death. Undoubtedly, these men ARE buried somewhere at Iuka:
1 TX Legion (27 TX Cav Co I) - Williford, Benjamin F. - 4 Cpl - DOW 8 Oct 1862 (WIA Iuka)
1 TX Legion (27 TX Cav Co A) - Mars, WIlliam - Pvt - DOW 12 Oct 1862 (WIA Iuka)
1 TX Legion (27 TX Cav Co I) - Knight, Samuel F. - Pvt - DOW 19 Oct 1862 (WIA Iuka)
1 TX Legion (27 TX Cav Co A) - Leftwich, J.C. - Pvt - DOW 12 Nov 1862 (WIA Iuka)
1 TX Legion (27 TX Cav Co C) - McKnight, James N. - Pvt - Listed as "Died" on muster roll for Sept-Oct 1862 (Prisoner Iuka)
1 TX Legion (27 TX Cav Co D) - Rhode, David J. - Pvt - DOW (no date) WIA/Prisoner Iuka
1 TX Legion (27 TX Cav Co C) - Pye, Benier - Pvt - Died (no date) Prisoner Iuka
Another four men have no records on file beyond their service at Iuka, and logically, could be buried there somewhere:
1 TX Legion (27 TX Cav Co K) - Ward, John - Pvt - WIA Iuka "Left behind" and "not heard from since" (no record of death or that he ever returned)
1 TX Legion (27 TX Cav Co D) - Marshall, Green B. - Pvt - WIA Iuka "Left in hospital" (no record of death or return)
1 TX Legion (27 TX Cav Co A) - Overall, William M. - Pvt - "Missing" Iuka (no record he was captured or ever returned)
1 TX Legion (27 TX Cav Co K) - Richie, R.J. - Pvt - WIA/Prisoner Iuka "paroled" and "not heard from since" (no record of return or death)
Five other casualties fit this time line, but unfortunately, no record of the location for these deaths were included in their files. Without the locations, it is equally POSSIBLE these men were buried by Confederate authorities rather than in the mass grave that was prepared by the Federal Provost Marshal, Capt. William Wiles:
1 TX Legion (27 TX Cav Co D) - Currey, Isaac - Pvt - Died Sept-Oct 1862 (no location/cause cited)
1 TX Legion (27 TX Cav Co C) - Callahan, Patrick - Pvt - Died Sept-Oct 1862 (no location/cause cited)
1 TX Legion (27 TX Cav Co C) - Jones, James R. - Pvt - Died Sept-Oct 1862 (no location/cause cited)
1 TX Legion (27 TX Cav Co M) - Stanifield, John - Pvt - Died Sept-Oct 1862 (no location/cause cited)
1 TX Legion (27 TX Cav Co M) - Thomas, James L. - Pvt - Died Sept-Oct 1862 (no location/cause cited)
As I said, this has been an intriguing project, involving so many units that I've never studied previously. It has been most interesting to branch out into new territory beyond my long study of the 37th Alabama Infantry who actually saw their first action of the war at Iuka alongside these brave Texans.