How do we tell whether 2 hiragana should fit in 1 "mora" or 2?

E.g.:

why is it that 四季 and 士気 are pronounced as "Shiki" 1 mora (audio), (audio)

whereas 式 and 指揮 are pronounced as "Shi Ki" 2 moras? (audio), (audio)

What I meant is according to the audio files i've linked to in the question, there is a significant difference in the "gap" between the two hiragana.

Why is it that although 式 and 四季 have the same hiragana (しき), 式 has both the clear sounds of "shi" and "ki" (2 distinct "sounds") whereas in 四季 the し and き are slurred to form a single "sound" ?

How do we tell whether 2 hiragana should fit in 1 "mora" or 2?

For example, why is it that 四季 and 士気 are pronounced as "Shiki" 1 mora, whereas 式 and 指揮 are pronounced as "Shi Ki" 2 morae? N.B. Links bring to a dictionary.

What I meant is that according to the audio files I've linked to in the question, there is a significant difference in the "gap" between the two hiragana.

Why is it that although 式 and 四季 have the same hiragana (しき), 式 has both the clear sounds of "shi" and "ki" (2 distinct "sounds") whereas in 四季 the し and き are slurred to form a single "sound" ?

How do we tell whether 2 hiragana should fit in 1 "mora" or 2?

E.g.:

why is it that 四季 and 士気 are pronounced as "Shiki" 1 mora (audio), (audio)

whereas 式 and 指揮 are pronounced as "Shi Ki" 2 moras? (audio), (audio)

Edit:

What I meant is this: according to the audio files i've linked to in the question, there is a significant difference in the "gap" between the two hiragana. For example, 式 has both the clear sounds of "shi" and "ki" whereas in 四季 the sounds are more or less ";slurred"

How do we tell whether 2 hiragana should fit in 1 "mora" or 2?

E.g.:

why is it that 四季 and 士気 are pronounced as "Shiki" 1 mora (audio), (audio)

whereas 式 and 指揮 are pronounced as "Shi Ki" 2 moras? (audio), (audio)

What I meant is according to the audio files i've linked to in the question, there is a significant difference in the "gap" between the two hiragana.

Why is it that although 式 and 四季 have the same hiragana (しき), 式 has both the clear sounds of "shi" and "ki" (2 distinct "sounds") whereas in 四季 the し and き are slurred to form a single ";sound" ?