Returning a cell value via matching 2 cells & rounding another down to match a third value

Hello all,

I have a problem that is doing my head in. I have a two sheet workbook (sample attached). sheet1 has 4 columns (titled SH, RS, RP and ID). The first two have data that is needed to match with data in sheet 2, the third column (RP) will usually never match sheet2, so via the formula I need, it will use this RP as an input, but not a matched input (I need it rounded down to the nearest match (round sheet1 RP down to the nearest sheet2 RP)). The fourth column in sheet1 is the one I need the formula for (the ID column).
The SH and RP values exist in both sheets. The RP values vary.
What I need the formula to do is, get the value from sheet1 in the SH column (say cell A2) and the RS value (B2), and the RP value (C2), and find the ID value in sheet2 where the SH and RS values are identical, and the RP in sheet1 is rounded down to match that in sheet2

So if sheet1 has:
SH = 2A
RS = 0
RP = 1.967
ID = (formula I need)

It will find in sheet 2:
SH = 2A
RS = 0
RP = 1.3 (sheet2 has 10 SH=2A / RS=0 entries as there are 10 RP values, and as RP=1.967 does not exist in sheet2, it rounds down to the nearest sheet2 RP which is 1.3)
Then from the above, returns the ID value from sheet2 (in this case 2662) in to sheet1 ID cell.

The above is row 8 information from the attached workbook.

So basically match the SH and RS for sheet1 and sheet2, get the RP in sheet1 and find the matching RP in sheet2 by rounding down the sheet1 RP to "match" sheet2 RP, and return the ID from sheet2 in to the ID in sheet1.

I hope that all made sense.

Thanking you all,

Simon