The /æ/ vowel is spelled <a> followed by two consonants or by one consonant in a monosyllable. The /ə/ (schwa) vowel can be spelled in many different ways, including replacing the reduced vowel with an apostrophe as in h'm.
The two sounds are both short and are both close together in the mouth, but the problem for learners with this pair lies not so much in the vowels themselves as in the assignment of stress. The schwa is always unstressed, which reduces the opportunities for making contrasts in the language as a whole. Indeed it can be argued that the abject/object group is not minimal since the stress pattern is different, and the name Ann will usually carry stress while the weak form indefinite article, here shown as 'un, never does. For learners of US English, this contrast overlaps with the vowel 4 versus vowel 10 contrast, cap/cup, since US English does not contrast the schwa with the /ʌ/ vowel.
The most interesting pair is malaise/Malays, though not every speaker will observe this distinction.
The mean density is almost too small to measure at less than 0.1%. The pairs make 6 semantic contrasts, giving a loading of 55%, but this is not significant on such a small group.
abject object abjection objection abjections objections Ann 'un am 'em ham h'm hammed h'mmed hamming h'mming hams h'ms malaise Malays topaz topers