We present several simultaneous multipoint measurements of energetic
ion events upstream of Earth's quasi-parallel bow shock by Cluster 
during time periods of large (1-1.5 Re) inter-spacecraft separation
distances. The e-folding distances of partial ion densities were 
determined by using a dynamical model bow shock surface. 
In the focus of our investigation is the scattering mechanism of
diffuse ions by waves which are to be found in the foreshock region.
Our results show that during times when the IMF is characterised 
by substantial directional stability the intensity of the 
Field Aligned Beam (FAB) is high. This high-intensity FAB 
generates waves which are convected deep in the foreshock 
region and strongly affects the scattering of diffuse ions 
which ultimately results in unusually low e-folding distances 
in the case of lower energy (10-18 keV) diffuse ions. 
These new results show that under different interplanetary 
conditions the scattering of diffuse ions (which leads to 
ion acceleration at the bow shock) can change significantly 
and this helps us to understand more the deeply the diffusive
acceleration mechanism at the Earth’s bow shock.