adjusting chart axis scale

In a report, I have a chart based on a parameter query. The horizontal(x)
axis is Months and the vertical(y) axis is average revenue for sales
managers. The criteria of the parameter query is sales managers, say SM1,
SM2, SM3, SM4. The variation of values for these across Months is as follows:
SM1: $71-$82, SM2: $72-$84, SM3: $66-$86, SM4: $62-$81
I am trying to adjust the scale of y axis such that the chart is able to
reflect the variation to the maximum extent and adjust the scale
automatically according to the values. For this, I set the scale of Y-axis to
auto for all, ie. max, min, major unit, minor unit, category x-axis crosses
at. When I run the reports, I observe that for SM1 and SM2, the scale adjusts
for a min 65, max 85, interval:5 and the x-axis crosses at 65. But for SM3
and SM4, it adjusts to min 0, max 100, interval: 20, x-axis crossing at 0.
The auto adjustment for SM1 and SM2 makes sense but for SM3 and SM4, I was
expecting a narrower range of scale, something like min 60 and max 90. How
can I do this?