If you dilute a solution by 4 times, it will be 0.25 of the original. If you dilute 1 part with 4 parts, it will be 0.20 of the original.
The exact meaning of your 1:4 needs to be known. Adding one volume to four volumes results in a final or five volumes. Simply adding solvent (diluting) until the final volume is 4 times the original is really a 1:3 mixture.
In the first case the concentration is 1/(1+4) ; 1/5 = 0.20.
In the second case it is 1/(1+3) ; 1/4 = 0.25.