1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

if __name__=='__main__':
    t=int(input())
    for i in range(t):
        n=int(input())
        a=list(map(int,input().split()))
        ind=[]
        for i in range(0,len(a)-1):
            if a[i]>a[i+1]:
                ind.append([i,a[i]])
            else:
                pass
        for i in range(len(a)-1,0,-1):
            if a[i]>a[i-1]:
                if i not in ind:
                    ind.append([i,a[i]])
            else:
                pass
        if ind:
            #print(ind[0]+1)
            ind=sorted(ind,key=lambda x: x[1],reverse=True)
            print(ind[0][0])
        else:
            print(-1)
            #print(ind)