there is more than one answer to this
when using dictionary attack (as you are doing right now), you can combine your dictionary with rules, see
https://hashcat.net/wiki/doku.php?id=rule_based_attack
so in your case this would be a rule-file with just 2 rules
$X
$x
this tells hashcat to append one upper X or lower x to each pw-candidate you are trying
or when using mask-attack you can specify up to 4 different charset so
-1 Xx and mask ?a?a?a?a?1 means 4 times all possible chars, 5th char only X or x
EDIT:
Hashmode: 14600 - LUKS (Iterations: 163044)
Speed.#1.........: 3079 H/s (89.54ms) @ Accel:32 Loops:512 Thr:512 Vec:1
Speed.#2.........: 2833 H/s (44.74ms) @ Accel:8 Loops:1024 Thr:512 Vec:1
Speed.#5.........: 337 H/s (57.12ms) @ Accel:512 Loops:256 Thr:1 Vec:4
Speed.#*.........: 6249 H/s
not a real cracking rig, but luks is just slow...
when using dictionary attack (as you are doing right now), you can combine your dictionary with rules, see
https://hashcat.net/wiki/doku.php?id=rule_based_attack
so in your case this would be a rule-file with just 2 rules
$X
$x
this tells hashcat to append one upper X or lower x to each pw-candidate you are trying
or when using mask-attack you can specify up to 4 different charset so
-1 Xx and mask ?a?a?a?a?1 means 4 times all possible chars, 5th char only X or x
EDIT:
Hashmode: 14600 - LUKS (Iterations: 163044)
Speed.#1.........: 3079 H/s (89.54ms) @ Accel:32 Loops:512 Thr:512 Vec:1
Speed.#2.........: 2833 H/s (44.74ms) @ Accel:8 Loops:1024 Thr:512 Vec:1
Speed.#5.........: 337 H/s (57.12ms) @ Accel:512 Loops:256 Thr:1 Vec:4
Speed.#*.........: 6249 H/s
not a real cracking rig, but luks is just slow...